This resubmission of a renewal application proposes studies to elucidate key mechanisms that regulate the function of the two ?3 integrins, ?IIb?3 and ?V?3, and should apply to integrins n general. Analyses will be performed to define the molecular mechanisms, which regulate the functions of these integrins and govern their contribution to the adhesive and migratory properties of cells. The target cells for analysis will be primarily endothelial cells and myeloid cells but will be relevant to all blood cells including platelets. These cells are all exposed to blood and the functions of their integrins must be tightly regulated to prevent uncontrolled binding of their plentiful ligands. The integrin regulatory molecules of emphasis are kindlin-2 and kindlin-3 and talin. Kindlins and talin control the activation of the integrins. Understanding the structure and function relationships that determine the activities of these molecules, their mechanisms of action, and the signaling pathways which regulate their function are primary objectives of the program. The emphasis of these studies will not only be on their role in controlling inside-out signaling, i.e., integrin activation, but also on their role in outside-in signaling via their regulation of the actin cytoskeleton. Additionally, the strategies proposed wil allow identification of entirely novel functions of the kindlins unrelated to integrins. The Progrm consists of three projects, each directed by an independent and productive faculty member in The Department of Molecular Cardiology at the Cleveland Clinic. Dr. Edward F. Plow, Ph.D., will serve as Program Director and lead Project 1. This project deals with the mechanism by which kindlin-2 regulates inside-out and outside-in signaling across integrins and exerts its integrin-independent functions. In Project 2, Dr. Jun Qin will use high resolution structural approaches to determine how talin and kindlin-2 regulate integrin activation, exploring what seem to be paradigm shifting leads. The regulation of the integrin activating and actin binding functions of talin will also be dissected. Dr. Tatiana Byzova leads Project 3 and focuses how kindlin-3 regulates the integrins. The focus of her studies will be how integrin regulation by kindlin-3 in endothelial and myeloid cells contributes to angiogenesis. The Program is supported by two Scientific Cores, Imaging and In Vivo (SC1), and Protein Expression and Mutagenesis (SC2) as well as by an Administrative Core (AC1). A common objective of the Program is to continue and create new collaborations among the Projects to resolve the structural and biological mechanisms that regulate the functions of the ?3 integrins. The information derived from these studies will provide insights into the complex and biologically important responses regulated by integrins and their activation that are relevant to thrombosis, angiogenesis and other cardiovascular diseases.